Method for producing a flat gas discharge lamp

ABSTRACT

A process for producing a discharge vessel of a flat gas discharge lamp, in which the discharge vessel has a base plate ( 1 ), a frame ( 3 ) and a cover plate ( 2 ), as well as at least one spacer ( 6 ) between base plate ( 1 ) and cover plate ( 2 ). At least between one of the plates ( 2 ) and the frame ( 3 ), at least one space ( 6 ) is initially kept open as a filling opening. By partial fusion of at least a part ( 4, 5 ) of the frame, which may also comprise a layer ( 4 ) of soldering glass and local elevations ( 5 ), the filling opening ( 6 ) is eliminated after the filling operation. The distance between the vessel plates ( 1, 2 ) is defined by the spacers ( 7 ), which remain hard even during the joining operation.

TECHNICAL FIELD

The invention relates to a process for producing a discharge vessel of aflat gas discharge lamp.

In particular, the invention is directed at the production of flat gasdischarge lamps which are designed for dielectric barrier discharges, inwhich, therefore, at least the electrodes of one polarity are separatedfrom the discharge volume in the discharge vessel by a dielectric layer(dielectric barrier discharge lamps).

Lamps of this type are suitable not only for general lighting but alsofor the backlighting of liquid crystal displays (LCDs) and fordecorative and advertising purposes.

PRIOR ART

Flat gas discharge lamps of the generic type have a discharge vesselwhich is formed by a base plate, a cover plate and a frame arrangedbetween them. It should be noted that in the present application thetechnology of flat gas discharge lamps for dielectric barrier dischargesis assumed to form the prior art. Moreover, by way of example, referenceis made to document WO98/43277, the content of disclosure of which withregard to the technology of flat gas discharge lamps for dielectricbarrier discharges is hereby incorporated by reference.

A flat discharge lamp of the generic type is known from DE 198 17 478A1. The discharge vessel of this lamp comprises two plates which areparallel to one another, a frame and spacers which support the twoplates with respect to one another. Each spacer comprises a componentwhich has a high viscosity and a component which has a low viscosity atthe joining temperature. Before the discharge vessel is joined together,the vertical dimension of each spacer is greater than the intended finalspacing between the two plates. The peripheral gap-like opening which isinitially kept clear as a result is used as a pump or filling openingfor the discharge vessel. When the discharge vessel is being joinedtogether, in each case the low-viscosity component of each spacercompensates for possible local deviations in the distances between thetwo plates.

EXPLANATION OF THE INVENTION

It is an object of the present invention to provide an improved processfor producing discharge vessels of gas discharge lamps.

This object is achieved by a process having the features of claim 1.

Preferred configurations of the invention form the subject matter of thedependent claims.

According to the invention, during production at least one space isinitially held open at least between one of the two discharge vesselplates and the frame, to act as a pump and filling opening. After purgegases and possible volatile contaminants have been pumped out and thevessel has then been filled with the fill gas or gases, for exampleXenon, the filling opening is eliminated as a result of at least part ofthe frame being partially fused. Moreover, at least one spacer isarranged between base plate and cover plate, for example in the form ofa ball, column or the like. During the joining operation describedabove, the spacers are not softened or fused at all, but rather remainhard. This ensures that the distance between base plate and cover plateis defined by the vertical dimension of the or each spacer.

Compared to the prior art, it is in this case possible to dispense withthe low-viscosity component of the spacers. Particularly in the case oflarge-area lamps or lamps with relatively thin vessel plates, whichconsequently require a relatively large number of spacers for stabilityreasons, this represents a considerable saving on material andmanufacturing outlay.

The discharge vessel individual parts are usually joined in a furnace.At the joining temperature, which is typically a few hundred degreesCelsius, for example approx. 500° C., according to the invention theframe or at least the appropriate part of the frame then softens, butthe two vessel plates and the spacers do not. To achieve this effect,the frame or that part of the frame which is intended to soften, whichmay also comprise a separate layer of soldering glass or a localelevation, is selected from a material with a viscosity which isrelatively low, for example approx. 10⁶ dPa s (dezi-pascal second) orless, at the joining temperature. Examples of suitable materials includesoldering glass or sintered glass materials, for example comprisingPb—Si—B—O, Bi—Si—B—O, Zn—Si—B—O, Zn—Bi—Si—B—O, Sn—Zn—P—O. By contrast,the two vessel plates and the spacers, as well as, if appropriate, theremaining part of the frame are selected from a material with aviscosity which is relatively high, for example approx. 10¹⁰ dPa s ormore, at the joining temperature. Examples of suitable materials forthis purpose are soft glass materials and crystallized soldering glassmaterials or composite solders and stable soldering glass materials witha high softening point, e.g. Bi—Si—B—O, Sn—Zn—P—O, Zn—B—Si—O, Pb—B—Si—Oand Zn—Bi—Si—B—O.

By way of example, the filling opening can be produced by selecting theheight of the spacers to be greater than the height of the uniformlysurrounding frame. The result is a gap between the frame and one of thetwo plates. After the filling operation, the gap is closed by softeningor partial fusion of the frame. If the frame is joined to the uppercover plate, i.e. the gap is between the base plate and the frame, theclosing operation is assisted by the forces of gravity, so that in thisway it is possible to close up even relatively large gaps withoutproblems. Further details in this respect are given in the descriptionof the exemplary embodiments.

As an alternative, the filling opening can be produced by a sealingsurface between one of the vessel plates and the frame being uneven. Byway of example, the sealing surface may be corrugated or may be elevatedat at least one distinct point. Suitable elevations are, for example,prefabricated sintered glass parts which are arranged on the frame.Alternatively, the elevations may also be formed integrally with theremaining part of the frame. By way of example, the elevations can alsobe produced as a result of the frame being assembled from individualparts, if the joins between the individual parts have previously beenpartially fused, for example by means of a laser. In this case, theelevations are formed from the partially fused material during joiningof the individual frame parts.

DESCRIPTION OF THE DRAWINGS

In the text which follows, the invention is explained in more concreteterms on the basis of a plurality of exemplary embodiments; the featuresdisclosed during this explanation may be pertinent to the invention bothindividually and in combinations other than those illustrated. In thedrawings:

FIG. 1 shows a diagrammatic side view of a flat radiator dischargevessel before the inventive closure, according to a first exemplaryembodiment in accordance with the invention,

FIG. 2 shows a diagrammatic side view of a further exemplary embodimentof the invention,

FIG. 3 a shows a diagrammatic side view of a third exemplary embodimentof the invention,

FIG. 3 b shows a plan view of the exemplary embodiment shown in FIG. 3 aon line AB,

FIG. 3 c shows a view of the exemplary embodiment shown in FIG. 3 a asseen in the direction of arrow C,

FIG. 4 shows a diagrammatic side view of a fourth exemplary embodimentof the invention.

The first exemplary embodiment, which is shown in FIG. 1, has a baseplate 1 and cover plate 2, and also a frame 3 made from soft glass. Theframe 3 may be joined to the base plate 1 in various ways or may beformed integrally therewith. In particular, it could also be joined tothe base plate 1 by partial glass fusion caused by light radiation(joining by means of laser radiation). The resulting discharge vessel issubstantially rectangular in cross section and its contour (not shown)is also rectangular. It is used to produce a flat radiator withdielectric barrier discharges for backlighting of a flat screen or forgeneral lighting purposes. Accordingly, electrode strips are printedonto that side of the base plate 1 which lies at the top in the figure,inside the frame 3, some of the electrodes being covered with adielectric layer. These details are of no further interest here and aretherefore not shown. Reference is made to the content of the disclosureof WO98/43277, which has already been cited.

However, the exemplary embodiment shown in FIG. 1 serves to illustratethe way in which the cover plate 2 is connected to the frame 3. For thispurpose, a layer of soldering glass with upper side 4 is applied to theframe 3 and, in the corners of the discharge vessel, is locally elevatedby means of small columns 5 of sintered glass. In the remaining region,the cover plate 2 lies above the top side 4 of the support, i.e. thesealing surface, at a distance which corresponds to the difference inheight between the columns 5 and the remaining support 3.

In this exemplary embodiment, columns 5 are provided in all four cornersof a flat radiator discharge vessel of rectangular contour. Accordingly,four spaces 6 result between the sealing surface 4 and the cover plate2, in each case corresponding to one side of the rectangular contour.The height of the columns 5 can also be adapted according to the demandsimposed on the line cross section for evacuation and filling of thedischarge vessel.

Four column-like spacers 7 made from soft glass (only two of which arevisible) are arranged standing on end, at uniform distances from oneanother, on the base plate 1.

After the operation of filling with the fill gas—in this case xenon—theindividual parts described above are joined to form the discharge vesselby heating in a furnace (not shown). The temperature in the furnace isincreased to such an extent that the soldering glass 4 and the sinteredglass columns 5 soften, i.e. adopt a viscosity of typically less than10⁶ dPa s. As a result, the cover plate 2 sinks onto the sealing surface4 of the frame 3 or the spacers 7. In this way, full closure of thedischarge vessel is achieved over the entire upper periphery of theframe 3, i.e. over the entire sealing surface 4. This typically requirestemperatures of 520° C. The distance between cover plate 2 and baseplate 1 results from the height of the hard spacers 7, the viscosity ofwhich is typically more than 10¹⁰ dPa s at the joining temperature.

This embodiment is preferably used for frame heights of over approx. 3mm. A further advantage is that the size of the pumping or fillingopening 6 can be influenced relatively easily by means of the height ofthe columns 5.

In a variant (not shown) the frame is assembled from at least twoindividual parts made from crystallized soldering glass or compositesolder, for example Bi—Si—B—O, Sn—Zn—P—O, Zn—B—Si—O or Zn—Bi—Si—B—O, inone plane. For this purpose, the individual frame parts are fusedtogether in a vacuum-tight manner by means of sintered-glass parts, e.g.comprising Pb—Si—B—O, Sn—Zn—P—O, Bi—B—Si—O or Zn—Si—B—O. Thesintered-glass parts are deliberately selected to be higher than theindividual frame parts. The elevations of the frame produced in this wayresult in spaces for filling, in a similar way to the exemplaryembodiment above. At their sealing surfaces, the individual frame partsare provided with a sintered-glass layer. At the joining temperatureduring the joining operation in the furnace, the individual frame parts,the two plates and the spacers remain hard, whereas the sintered-glasslayer and the sintered-glass parts soften. This causes the cover plateto sink onto the appropriately dimensioned spacers in such a manner thatthe filling opening is closed as a result of frame and vessel platebeing joined together.

This variant is also preferably used for frames of heights of overapprox. 3 mm. Moreover, this frame comprising a plurality of individualparts is less expensive than a single-part frame.

A further exemplary embodiment, relating to a flat radiator of the typementioned in the first exemplary embodiment, is shown in FIG. 2. In thiscase, a frame 8 between the base plate 1 and the cover plate 2 consistsof soldering glass (at least in the upper region). The upper region ofthe frame 8 and the sealing surface 4′ resting thereon are corrugated,so that the cover plate 2 bears against the frame 8 at a relativelylarge number of locations, between each of which there are individualfilling openings 9—corresponding to the valleys of the corrugation. As aresult of at least the upper region of the frame 8 being softened orpartially fused, in particular in the region of the crests of thecorrugation, in this case too the cover plate 2 sinks onto the sealingsurface 13′ with surface-to-surface contact, thereby closing thedischarge vessel. The desired distance between cover plate 2 and baseplate 1 is in this case too produced by the suitably selected height ofthe spacers 7, which remain sufficiently hard at the joiningtemperature.

One advantage during production is the more stable position of the coverplate, on account of the numerous contact locations (corrugationcrests). Moreover, it is in this way possible to achieve more uniformlowering of the cover plate during the joining phase. The risk of thecover plate being displaced or slipping is considerably reduced.However, the relatively high precision which is required duringproduction of the frame represents a drawback.

FIGS. 3 a, 3 b, 3 c show a diagrammatic side view, a plan view on lineAB and a view as seen in direction C of a third exemplary embodiment ofthe invention. In this case, a frame between the base plate 1 and thecover plate 2 comprises four straight individual parts 10 a–10 d madefrom soldering glass. The first two individual frame parts 10 a, 10 bare arranged parallel to one another directly on the base plate 1(forming a first layer). The remaining two individual frame parts 10 cand 10 d are in each case at right angles thereto and are placed onto ineach case one end of the first two individual frame parts 10 a, 10 b(second layer). In this way, the cover plate 2 is initially arranged ata distance of twice the height of each individual part 10 a–10 d fromthe base plate 1. In this case, the four gaps 11 a–11 d—two in each ofthe two layers—which are formed as a result of the two times twoindividual frame parts 10 a, 10 b and 10 c, 10 d being in layers whichare offset by 90°, function as filling openings.

Five column-like spacers 12 are arranged standing on end and at constantdistances from one another on the base plate 1. The cross section ofeach spacer 12 is in the form of a cross. With a view to minimizing thevisibility of the spacers 12 when the illuminating cover plate 2 islooked at, this shape has proven appropriate.

The joining of the individual parts described above to form thedischarge vessel takes place in a similar way to the method describedabove, through heating in a furnace (not shown). When the individualframe parts 10 a–10 d soften or partially fuse, the two upper individualframe parts 10 c, 10 d, including the cover plate 2, sink downward andthereby close off the discharge vessel. The desired distance betweencover plate 2 and base plate 1 is once again produced by anappropriately selected height of the spacers 12, which are stillsufficiently hard at the joining temperature.

An advantage of this embodiment is that the individual parts can beprefabricated. Moreover, pour-free glass bodies, with consequentlyreduced outgasing during the joining phase, can be used for thispurpose. Consequently, it is possible to achieve a better purity of gaswithin the closed discharge vessel. A drawback is the relativedifficulty of positioning the individual frame parts. Moreover, thefilling openings are restricted to the height of the individual frameparts.

The fourth exemplary embodiment, which is diagrammatically illustratedin FIG. 4, has a base plate 1 and a cover plate 2 made from soft glass.Five column-like spacers 7 (only three of which are visible) made fromsoft glass are arranged standing on end on the base plate 1. The coverplate 2 rests on the spacers 7. A frame 13, which is connected to thecover plate 2, is arranged between base plate 1 and cover plate 2. Itsheight is deliberately selected in such a manner that initially a gap14, which functions as a filling opening, remains between the frame 13and the base plate 1. The frame 13 consists of soldering glass.

After the filling operation, the discharge vessel is closed in agastight manner by heating in a furnace. In the process, the softenedframe 13 moves downward to the base plate 1, so that the latter isjoined to the frame 13.

After controlled cooling (to avoid stresses), the discharge vessel issuitable for further use.

This embodiment is preferably used for frame heights of up to approx. 3mm. This is a relatively inexpensive process. The frame may be applieddirectly to the cover plate, initially in paste form, for example bymeans of a dispenser. In the process, the frame can be shaped asdesired. Moreover, it is possible to produce different frame contours,for example round or polygonal. However, a drawback is that there isusually a high level of outgasing of the frame paste during the joiningprocess. This may have an adverse effect on the gas purity. Moreover, arelatively precise temperature control is required during the joiningprocess.

1. A process for producing a discharge vessel of a flat gas dischargelamp, comprising: (a) forming an assembly of a base plate, at least onespacer, a frame and a cover plate, the frame comprising first and secondlayers each having two straight individual frame parts that are arrangedparallel to and at a distance from one another, the individual frameparts of the first layer being arranged on the base plate and at rightangles to the individual frame parts of the second layer, ends ofindividual frame parts of the second layer being placed on ends of theindividual frame parts of the first layer so that two filling openingsare formed in each layer, the cover plate being arranged on the frame,(b) filling the assembly with a gas, (c) heating the assembly at ajoining temperature to soften the individual frame parts, close thefilling openings and join the frame parts to each other and to the baseand cover plates, the at least one spacer remaining sufficiently hardduring the heating to define a distance between the cover plate and theback plate.
 2. The process of claim 1 wherein the individual frame partsare made of a soldering glass.
 3. The process of claim 1 wherein the atleast one spacer has a viscosity of more than 10¹⁰ dPa s at the joiningtemperature.
 4. The process of claim 1 wherein the individual frameparts have a viscosity of less than 10⁶ dPa s at the joiningtemperature.
 5. A process for producing a discharge vessel of a flat gasdischarge lamp, comprising: (a) forming an assembly of a base plate, atleast one spacer, a frame and a cover plate, the frame being joined tothe base plate and having a sealing surface, the cover plate beingspaced apart from the sealing surface by columns in order to formfilling openings between the cover plate and the frame, (b) filling theassembly with a gas, (c) heating the assembly to a joining temperatureto soften the columns in order to cause the cover plate to contact theat least one spacer, join the cover plate to the frame, and close thefilling openings, the at least one spacer remaining sufficiently hardduring the heating to define a distance between the cover plate and theback plate.
 6. The process of claim 5 wherein the discharge vessel issubstantially rectangular and the columns are located at each corner ofthe discharge vessel.
 7. The process of claim 5 wherein the sealingsurface is comprised of a layer of soldering glass.
 8. The process ofclaim 7 wherein the columns are comprised of a sintered glass.
 9. Theprocess of claim 5 wherein the at least one spacer has a viscosity ofmore than 10¹⁰ dPa s at the joining temperature.
 10. A process forproducing a discharge vessel of a flat gas discharge lamp, comprising:(a) forming an assembly of a base plate, at least one spacer, a frameand a cover plate, the frame having a sealing surface, the sealingsurface being uneven and contacting the cover plate whereby fillingopenings are formed between the sealing surface and the cover plate, (b)filling the assembly with a gas, (c) heating the assembly at a joiningtemperature to close the filling opening and join the cover plate to theframe, the at least one spacer remaining sufficiently hard during theheating to define a distance between the cover plate and the back plate.11. The process of claim 10 wherein the sealing surface is corrugated.12. The process of claim 10 wherein the sealing surface is comprised ofa soldering glass.
 13. The process of claim 10 wherein the at least onespacer has a viscosity of more than 10¹⁰ dPa s at the joiningtemperature.
 14. The process of claim 13 wherein the sealing surface hasa viscosity of less than 10⁶ dPa s at the joining temperature.
 15. Aprocess for producing a discharge vessel of a flat gas discharge lamp,comprising: (a) forming an assembly of a base plate, at least onespacer, a frame and a cover plate, the frame being joined to the coverplate, the base plate being spaced apart from the frame by the at leastone spacer whereby a filling opening is formed between the base plateand the frame, (b) filling the assembly with a gas, (c) heating theassembly at a joining temperature to soften frame, close the fillingopening, and join the base plate to the frame, the at least one spacerremaining sufficiently hard during the heating to define a distancebetween the cover plate and the back plate.
 16. The process of claim 15wherein the frame is comprised of a soldering glass.
 17. The process ofclaim 15 wherein the frame has a viscosity of less than 10⁶ dPa s at thejoining temperature.
 18. The process of claim 15 wherein the at leastone spacer has a viscosity of more than 10¹⁰ dPa s at the joiningtemperature.
 19. The process of claim 18 wherein the frame has aviscosity of less than 10⁶ dPa s at the joining temperature.